1. Field of the Invention
The present invention relates to a liquid tank which is capable of detecting a liquid level of liquid, such as gasoline.
2. Discussion of the Background
As an example of such a liquid tank, there is known a fuel tank for reserving gasoline for vehicles. Generally, the fuel tank is provided with means for detecting a surface level of the gasoline. The level detecting means comprises a float on the gasoline, an arm for converting a high and low position of the float into a rotational position of the arm, and a potentiometer (sensor) for converting the rotational position of the arm into electric signals.
In the above-mentioned fuel tank, the surface of gasoline often inclines by the vehicle's acceleration, deceleration, rolling or the like. Further, by the vehicle's vibration, the surface of gasoline sometimes undulates and inclines and the gasoline scatters as the case may be.
Thus, it should be noted that in the above fuel tank, the level of gasoline is usually changeable. Therefore, if an output of the potentiometer is introduced into a not-shown fuel indicator directly, a pointer indicating the residual amounts is so changeable that it is hard for a driver to see. Accordingly, in order to obtain the mean value of the residual gasoline, there has been taken some measures that a responsibility of the fuel indicator is purposely decreased and that a resistance plate for resisting the motion of gasoline is arranged in the fuel tank.
In addition, because of its easiness for vaporization, a space on the upside of the tank is filled with the vaporized gasoline. Therefore, when the gasoline is charged into the fuel tank, the vaporized gasoline in the tank will be discharged in the air through a return pipe.
In order to solve the problem, there has been developed a fuel tank in which an expandable bag is arranged in a tank body, while the gasoline is supplied into the bag. In the fuel tank having the above bag, since the gasoline does not come in contact with the air, the gasoline is not vaporized and discharged in the air.
In the above fuel tank, however, an upper position of the bag changes greatly since the gasoline moves in the form of a packed bag. Accordingly, it is necessary to decrease the responsibility of the fuel indicator for purposes of obtaining an average of the residual amounts of the gasoline. Note, due to the bag, it is impossible to arrange the above resistance plate in the tank body.
Further, despite of the decrease in responsibility of the fuel indicator and the provision of the resistance plate, if the automobile is left on a slope as it is, the fuel surface will incline with time passing, so that the fuel indicator displays erroneous residual amounts just as calculated. Therefore, the conventional fuel tank has a problem of producing a great error in residual amounts of the gasoline, particularly, on the slanted load.
On the other hand, in the above-mentioned fuel tank having the bag therein, there is a problem that the bag is easy to be injured because the bag has a large surface area and moves while rubbing against the inner face of the tank body with an movement of the gasoline.